Check the permissions/owner of the authorized_keys file. I’m not at home right now to give you the path to it, but I have had a similar problem after I add a new ssh key to my gitea/forgejo account. It often turns out that in doing so, sometime the permissions change and gitea/forgejo then refuses to use the file.

In my case the problem is probably rooted within the uid/gid thats used inside the container and/or the nfs mount I use for the container volume. I never bothered to get to the bottom of it though.